Each year the redosier dogwood (Cornus sericea) in the yard is host to the caterpillars of the dogwood sawfly (Macremphytus tarsatus). The sawfly is far better known by its distinctive larval caterpillar; the adult is a small wasp-like fly whose picture I couldn't find on a quick search of the internet. The larvae are a real pest on this red-twig dogwood; they can strip all the leaves off in a couple weeks.
The smallest stage of the caterpillar usually goes unnoticed. By the time they are in their second stage they are covered with a waxy white coating that makes them look like, well, bird droppings—likely a good protection from birds. By this time they are eating many of the leaves down to the midvein.
By the third stage they are yellow and black, a pattern that may offer camouflage as they eventually disperse to locate overwintering sites on the forest floor, according to Johnson & Lyon in Insects that Feed on Trees and Shrubs (Cornell University 1991, p. 126).
The authors note that they also overwinter in wood-fiber wallboard and clapboard siding, and that woodpeckers can detect their presence and cause damage in their feeding. Uh oh, I have seen them climbing the stucco walls of the house toward the cedar siding above.
Most years I have controlled some of them with a strong spray from the hose or knocking them off into a coffee can filled with soapy water. The goal of this IPM, or integrated pest management, is to reduce the damage to a tolerable threshold using means with the least harm to the environment.
